1. Field of the Invention
This invention relates to froth flotation cells which are used to beneficiate mineral ores by separating selected value specie components from a composite. Specifically, this invention relates to structural means for improving froth removal dynamics in flotation cells.
2. Statement of the Art
Froth flotation cells are widely known and used in a variety of industries to preferentially separate particulates or other suspendable species from each other thereby upgrading the product grade. Flotation cells are most commonly used in metallurgical and mining operations, but are used in many other industries. Selective solids separation in a flotation cell is accomplished by mixing air (bubbles) with suitably prepared mineral in fluid to facilitate attachment of a floatable specie to an air bubble which then rises to the top of the fluid volume for removal at or near the top of the tank. Froth is produced by the introduction of air into the fluid or slurry with the resulting attachment of selected particles to the air bubbles produced. The air bubbles, with floatable particles attached, float to the top of the fluid volume the tank and produce a layer or phase of froth which contains the floatable specie. The froth is then removed via an overflow weir positioned near the top of the fluid volume. Froth may also be produced or enhanced by the addition of frothing agents.
Flotation cell technology has focussed on various aspects of froth flotation mechanics in an effort to optimize methods and efficiencies of separation. All flotation cells generally comprise the same principal elements, namely a tank sized for retaining a volume of fluid, an inlet or influent feed source, a means of introducing air or another gas into the fluid volume, and an overflow weir near the top of the tank to receive the froth formed on the fluid volume. Typically, flotation cells will include an underflow conduit or other outlet to remove fluids and non-floatable separated solids near the bottom of the cell or tank.
In operation of a flotation cell, an influent feed is introduced into the tank, usually at or near the bottom of the tank. A stator-rotor structure is centrally positioned in the tank relative to the vertical axis of the tank when viewed in a plan view. Air is introduced into the flotation cell, either under pressure (i.e., forced air) or by natural ingestion of air by action of the rotor mechanism. Air bubbles are generated in the volume of circulated pulp within the tank and is mixed with the minerals therein. A stable air bubble matrix is formed where particles in the influent contact or adhere to the bubbles. The air bubbles rise to the top of the fluid volume and form a froth which flows into a launder positioned near the top of the tank. Examples of flotation cells comprising the basic elements and operations described are disclosed in U.S. Pat. No. 3,993,563 to Degner issued Nov. 23, 1976 and U.S. Pat. No. 4,737,272 to Szatkowski, et al., issued Apr. 12, 1988.
Modifications of the above-described basic elements of a flotation cell have been developed in an effort to maximize operation of the flotation cell, usually responsive to varying conditions in the influent feed or variations in the type or size of particulates contained in the influent. For example, U.S. Pat. No. 5,219,467 to Nyman, et al., discloses a modified flotation cell structured to provide increased agitation to the influent feed in order to improve selectivity of species in the separation process. The structure of the flotation cell includes means for introducing air into the bottom of the tank and shearing it to form bubbles which are then directed upwardly along the circumference of the tank by vertical flow guides. An agitation attenuator is positioned in the mid-section of the flotation cell to reduce the agitation process and to move flotation air to the outer circumference of the flotation cell.
Another example of a modified flotation cell which is structured to introduce wash water into the froth to remove interstitially entrapped gangue is disclosed in UK Patent Application No. 2 281 521, published Mar. 8, 1995. The disclosed flotation cell is structured with a porous diffusion surface positioned below the top of the tank which directs froth upwardly in the tank and introduces wash water to the upper portion of the froth. In a similar construction, U.S. Pat. No. 5,039,400, issued Aug. 13, 1991, discloses a modified flotation cell which is structured to reduce the area in which froth is formed to intentionally deepen, or extend the height of, the froth bed and thereby increase the residence time of the froth within the tank. A source of wash water is positioned within the froth bed to wash away impurities trapped in the froth.
The flotation cells described above, as well as many other flotation cell designs, are designed to optimize operation of the apparatus responsive to requirements of the influent feed liquid and the particulate matter profiles. Known flotation cell constructions heretofore have neither appreciated nor addressed the operational benefits which can be gained by providing a means for expediting removal of the froth from the flotation cell. Thus, it would be advantageous in the art to provide a flotation cell which is structured to facilitate removal of the froth from the flotation cell tank and thereby enhance the operation of the apparatus.